The use of wireless telephones and communications systems has become so widespread that they have become a fixture in everyday life. A significant percentage of the population subscribes to wireless telephone and/or communications service of one form or another. Wireless devices now offer more than simple voice. The user may be able to send and receive messages, browse the Internet, access computer networks, and so forth on a wireless device that is connected to a wireless communications system.
To support such a wide variety of different services, a large amount of data must be received at and transmitted from a wireless device and some of that data must arrive at the wireless device in a timely fashion. Data that is urgent in nature may often be sent at a higher priority than typical data. This highly urgent data may be sent at the expense of typical data. An example of high urgency message is a message that contains media-access control (MAC) state transitions. Its timely reception may be vital to the continued operation of the wireless device.
Some wireless communications systems support the use of messages with different frame durations. In such systems, typical communications will transmit data in frames of a specified duration and for messages of high-urgency, a shorter duration frame may be used. Shorter duration frames may be used to ensure that the high-urgency message be transmitted as soon as possible and to minimize disruption to normal message traffic. In an IS-2000 compliant communications system, for example, data is normally transmitted in frames with a 20 millisecond (ms) duration. However, highly urgent messages can be transmitted in a shorter duration frame. The shorter duration frame has a five (5) ms duration.
When the shorter duration frame is transmitted, it may simply be inserted into a first available 5 ms subframe of the 20 ms frame, obliterating any data that was in that particular 5 ms subframe. This method of transmission is referred to as puncturing, wherein the 20 ms frame has been punctured by the 5 ms frame. Unfortunately, the puncturing of the 20 ms frame by the 5 ms frame can make it more difficult to decode the frames at the receiver, especially if no frame duration indicator or flag is asserted. When no indication as to the currently arriving data's frame duration is provided in the signaling, the receiver does not know if it has received a 5 ms frame or a 20 ms frame. Therefore, receiver design may need to be made more complex when frame puncturing is supported.
A relatively straight forward approach to decoding received signals in a communications system that permits frame puncturing involves receiving each 5 ms subframe and decoding the 5 ms subframe as a 5 ms frame. At the same time, the received signal is buffered so that information is not lost in case the received data is actually part of a 20 ms frame. Then, when a complete 20 ms frame (four 5 ms subframes) have been received and it is determined that at least one of the 5 ms subframes is actually part of a 20 ms frame, the buffered data (with any actual 5 ms frame data eliminated) is decoded. If none of the four 5 ms subframes contain 20 ms frame data, then the 20 ms frame decoding need not be performed.
One disadvantage of the prior art is the decoding of the 20 ms frame cannot start until all four 5 ms subframes have been processed. This requires a 20 ms buffer which adds costs and increases power consumption.
A second disadvantage of the prior art is that once the four 5 ms subframes have been processed, the 20 ms frame decoding cannot begin until additional post deinterleave processing to the 20 ms frame data is performed. This adds additional latency to the 20 ms frame decoding.
A third disadvantage of the prior art is that additional hardware in the form of a burst post-processing deinterleaver, an additional memory interface, additional decoders, control hardware, and so forth is needed.
A fourth disadvantage of the prior art is that if during the frame transmission the transmitter enters discontinuous mode (DTX) after transmitting a 5 ms frame, the receiver cannot turn off its power to reduce power consumption.
A fifth disadvantage of the prior art is that although the shorter duration frame, for example, 5 ms, is always decoded, the majority of the data being received by the wireless device is in the longer duration frame format, for example, 20 ms. Therefore, a large amount of unnecessary processing is being performed.